Prevention of ice formation on aircraft



2 Sheets-Sheet l J. HALBERT ET ALV ////f/////////////// /h//.F/f

Y Filed March 17, 1945 PREVENTION OF ICE FORMATI-ON ON AIRCRAFT Dec. 23,1947.

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Dec. 23, 14947. J. HALBERT Er Al..

l PREVENTION OF ICE FORMATION ON AIRCRAFT I Filed March 17, 1943 2Sheets-Sheet 2 of larger diameter.

Patented Dec. 23, 1947 UNITED sTArEsfrATENT OFFICE PREVENTIQN OF ICEFORMATION O N AIRCRAFT Joseph Halbert and Ronald Rawson Rawson,Haltwhistle, England, assignors to Sheepbridge yStokes Gentri-fugalCastings Company Limited, Chestereld, England, a British companyApplication March 17, 1943, Serial No. .479,510

In Great Britain August 11, '1942 `11 Claims. (01144-134) xof liquids inequal'controlled amounts vover any- 'thing but fshort 4distances uhasxalways vbeen difficult.

To cause liquid to travel in a pipe La pressure headis required whichincreases-fas the distance to be 'travelled increases. `If the areaforthe passage of the `liquid can be made sufficiently large in comparisonwith the.:quantity of liquid `flowing, this pressure can :be .fmadeA.very small. Inpracticespace is always limited -for one reason oranother. Thus the distribution orices of whatever form they :'be,.-musthave `jsuitlcient `resistance to flow that vthe required 'amountof liquid per orice Vwillgivea sufficiently high pressure, that'thezpressure drop-necessary to pass the lquid'to'thefurther:distribution orifices .will be only a vsmallpercentagezoithertotalzpressure and `th'us 'not allow tooggrcat anflowfrom lthenearer orifices.

Another difliculty arises-when thefsmallness ofthe'owsrequires,very-fine orices. This can be seen when i it.is-"realised'` that a single e of ianV inch hole through aplate 1a-.ofTan inch thick will, at a pressure of only "2 lbs./-sq.in.,.havemanyrtimes `the flow 'required'fordeliveryovera-length of `frein -to 15stoet. 'Thus thedrilling of ne `holes in lengths"` of `pipeisi-mpossi-ble. -linV slots falso `vvoul'dhave to beofsuch-width'thatfimpossible tolerances y'would have .to be -worked to.come'by using Various :porous media, which Thus the difficulty hasusually "been overh'ave a porosity .tocgivethe Irequiredpressure Thefinenessfofthe -holesinecessary is always a source of `Weakness'owingato choking by'dust. -Even` when such 'materials yas porousV:metals are used, 'which :donot:deteriorate-With time in the `ordinaryway, arpressure risewith-.timeoccurs with manynliquids desirable forvusev as cle-icing media, due to lthe"very"1minute holes or `porespresent. This"rise of; pressure only :occurswwhen the holes throughwhich the liquid has to pass are 'of lminute".areafiandiidoessnotfoccurdn rholes p of Fig. 6, and

The problemis solved accordingfto the present invention by Vdividing itDinto two parts, which is effected by` rst dividing the -ow .of liquidso as to obtain distribution to -a reasonable numberv of parts, and,then obtaining .the nal spreading over to the surface to .be protected,by means of a porous material.

Accordingly, the Epresent yinvention provides means `for preventing therformation `of ice on aircraft `comprising :back `,pressure-producingtubes, means for .supplying an anti-freezing 4liquid thereto, lsaid.tubes =communicating with a chamber Vwhich s in .contact1witha.porous*material, whichis adapted to be mountedqadjacent that partof the aircraft ,Which Ait `:is desired to protect from the formation ofice.

The necessary .pressure maybe providedvby a pump, but other `means Jforproducing pressure such as a gravity feed .may be used ,if desired, 0rthe liquid may be'E stored in a, oorivenien'mroser- Voir under pressureandreleased as desired,

The .porous `material isnpreferably Ya ,mass `of porous metalbutrotherporous material such as wicking, cotton fabrics such V as cotton duck,linen, porous rubber, porous synthetic resinous masses, porous glass,porcelain, vvolcanic and ar- `tii'lcial stone, porous wood, metal gauze,Vfibrous materials, chalk, or glass-fibres covered by a -wire meshscreen may be used.

The invention vwill now`be further described by way ofeXamplewith-reference toft-heaccompanying drawings,in which:

Figure 1 -is asectionalviewof an apparatus according to the invention;

Fig. 2 is a section on line `rA---A of Figf-l; Fig. 3 is la section online '-B-Bof Fignl;

Fig. 4 is a View ofafdetail vshowing :one of lthe dams;

Fig. 5 is av'section on'line C-C ofFigA; Fig. 6 is a plan view-showingthe .-.apparatus according to theinvention itted tofan aircraft; Fig. 7is a sectionali-view takenon 'line'D-:D

Fig. 8 is awsectional :.viewrtaken on lineaE-,E of Fig. 6. f

According to the yfiiwentionzthe mea-nsgfor `preventing the formation ofice :on aircraft-0.9mprises a channe1.-s11aped- -.metalfmmbelthe jouterpart of Whichisflled with -afmassotporous metal, a chamberzbeingformedjbetween thelower surface of the porousymetala-nd the fbottomandlower sides of the ,channel-shaped member -and a plurality of AflowresistingLtubes `projecting' through therbottom of ethe chamber throughwhich the anti-freezing@liquid;is-supplied.`

Preferably dams are provided at intervals along the chamber. The spacingof these dams depends upon the pressure resistance through the porousmetal, the viscosity of the anti-freezing liquid and the angle of thewing slope (in the case in which a wing surface is being de-iced). Thehigher the resistance of the porous metal the smaller will be the numberof dams required and also the greater the viscosity of the antifreezingliquid the smaller will be the number of dams required. The greater theangle of the wing slope the greater is the number of the dams required.

Preferably also a larger bore tube is fittedover the end of the backpressure-producing tubes. This serves to prevent the backpressure-producing tubes from being blocked up during manufacture andalso helps to increase the number of points in the chamber to which theantifreezing liquid is positively led.

The porous metal must be securely attached and is preferably bonded tothe channel-shaped metal member. This may be effected, for example, bysoldering or b razing, riveting or screwing, or by forming the mass ofporous metal on the channel-shaped metal member as by sintering in sucha way that bonding takes place.

The tubes on entering the chamber are pref-i erably bent at right anglesand should have a bore of between 0.002 and 0.050 of an inch, preferablybetween 0.008 and 0.025 of an inch.

The anti-freezing liquid which passes into the chamber seeps through themass of porous metal which is disposed at or adjacent that part of theaircraft which it is desired to protect from ice formation.

The mass of porous metal is conveniently made from a metal powder by theprocesses known in the art of powder metallurgy. In choosing a metal forthe porous metal mass consideration should be given to the factors ofresistance to atmospheric corrosion and corrosion by the antifreezingliquid, and also the factors of mechanical strength and resistance tovibration.

Referring to Figs. 1 to 5 of the drawings, antifreezing liquid issupplied by a pump (not shown) to the chamber I which is provided with aplurality of tubes 2 each of about 0.017 of an inch bore which introducethe anti-freezing liquid into the chamber 3 in close proximity to themass of porous metal 4 through which the liquid seeps to that part ofthe aircraft which is to be protected. The end of the tube 2 issurrounded by a tube 5 and dams 6 are provided at about 12 inchintervals. The pump gives a constant delivery of liquid and, as thisquantity has to pass through a given number of the small bore tubes 2and a given pressure is needed to do this, the pump, being of constantdelivery type, will produce this pressure in the system. Thus, while itmay not be strictly correct to say that the small bore tubes producedthe pressure, their presence in the system is responsible for the pumpproducing the pressure.

The purpose of providing the tube 5 is for convenience of manufacture.Its object is to cover the outlet of the small bore tube and prevent thepowders from entering it and blocking it before sintering takes place.The bore of the tube is so great, that for the low flows needed, thepressure drop is negligible; in fact the pressure difference in incheshead of liquid kfor equal flow in a 1" and length cannot be readvisually without considerable magnification.

For this example of a tube of 0.017 of an inch bore, the length of thetube is 3 and this supplies 3" of porous metal. The figures will varycorresponding with variation in the bore of the tube. Thus, for example,for tubes of bores between 0.014 and 0.018, the tube length variesbetween 2 inches and 31/2 inches. The tube 5 varies from 1 to 3 inchesin length and the bore is Mg.

Referring now to Figs. 6 to 8 of the drawings, these illustrate theapparatus of the invention fitted to an aircraft. At various leadingedges of the aircraft indicated generally by the reference numeral 'Ithere are fitted a number of units 8 comprising a mass of porous metal,and means for supplying an anti-freezing liquid thereto such as thatillustrated in Figs. 1 to 5 of the drawings. It will be seen that insome cases a plurality of such units are employed. The anti-freezingliquid is contained in a tank 9 and is distributed to the Various units8 by the pump l0`and the feed pipes Il. The division of the unit nearthe tip into sections, as shown in Fig. 6, has the following purposes:

(1) to simplify manufacture and handling, by not having too long alength of distributor to deal with, and

(2) to prevent difcult alteration in the construction of the wing, whichthe presence of a groove to take the distribution would make necessaryat certain points, if it had to be carried straight through.

It will be understood that the expression metal as used herein includesalloys, and among metals which are suitable as constituents of theporous metal mass are nickel, nickel-copper alloys, copper-nickel-tinalloys, coppernickel-antimony alloys and stainless steel.

By varying the size of the pores and the degree of porosity it will bepossible to vary the pressure at which the anti-freezing liquid issupplied to the surface which it is desired to protect.

Thus the porous metal used should have a solid content of between 30 and80%, i. e. between '70 and 20% of voids. The pores are of the continuoustype and can be formed by the use of a volatile substance such asSteroteX (a vegetable shortening) or salicylic acid or stearine, whichform a gas or vapour during sintering. The powders and the volatilesubstance are mixed uniformly and when in place in the channel memberduring sintering, gas or Vapour will be evolved and will flow upwards.Porosity' can be varied by using different shapes and sizes of powder. Aspherical copper powder made by one process gave an entirely differentflow to an electrolytic copper powder made by another. By adjusting theshape and the limits of the size of the powders used it is possible toadjust the pressure produced by the flow required. It was found that thegreater the range of particle size the higher is the pressure requiredto give equal ow and vice-versa. Also the larger the particle sizewithin a given range the lower is the pressure necessary. By using alarger grain size lower melting point powder in admiXture with any givenparticle of higher melting point powder it was found that a smallernumber of large pores could be obtained, for example by using copper andnickel powders of 400 mesh and tin powder of between and 200 vretrawtabregg-Cama saryteprcvdeffon cert :drepithrough the. come metaluniformvliiow .infthe spacesbeiwe., Mythe `highest lt.emr@rature .at:which ite will fformigfise. 03 Crfitis advisable to l es @ressurenwhichwilli/give 1s with the.flowering;erA the .temneret the.viscositytoftheanti ezine higher and the liquid.requiresgreaten.rites to pump itover the system. At the same it must be seenfthat there at.Aday*i.temperature eig gm lCmto get suicient distribution to allowchecking up of the system on the grounds-Thelincreasein viscosity ofanti- .ireegnealiquids between the .temperature f time toornevenmorelrneans that with a pump pressure of 3-lbs.A/sqf. in.a,t.-15-LC.l a pressure The expression ack pressure producing tubes usedin the-claims is dened as small bore tubes connecting the conduit withthe chamber, of such bore and length as to act as a metering or controldevice for the quantity of liquid which it is desired to admit.

We claim:

1. An aeronautical structural element disposed at the leading edge of anairfoil of aircraft comprising a series of chambers having wall portionsof rigid porous material the outer surfaces of which wall portions aremounted adjacent that part of the aircraft which it is desired toprotect from the formation of ice, a conduit substantially co-extensivewith said series of chambers for conveying iluid under pressure, andflow resisting tubes connecting said conduit with said chambers theporosity of said porous material being such that in the absence of saidflow resisting tubes the fluid would not reach all said chambers.

2. An aeronautical structural element disposed at the leading edge of anairfoil of aircraft comprising a series of chambers having wall portionsof rigid porous metal the outer surfaces of which wall portions aremounted adjacent that part of the aircraft which it is desired toprotect from the formation of ice, a conduit substantially coextensivewith said series of chambers for conveying uid under pressure, and owresisting tubes connecting said conduit with said chambers the porosityof said porous material being such that in the absence of said flowresisting tubes the fluid would not reach all said chambers.

3. An aeronautical structural element disposed at the leading edge of anairfoil of aircraft comprising a series of chambers having wall portionsof rigid porous material the outer surfaces of '.-isasufflcient pressure'df said owresi ing 'tubes me huid would "net t duitwithsaicch rs., `tiebore of said flow resisting tubes being small'rlative to the dimensionsof the chambers the porosity of said porous material being such that inthe absence of said ow resisting tubes the uid would not reach all saidchambers.

6. An aeronautical structural element disposed at the leading edge of anairfoil of aircraft cornprising a series of chambers having wallportions of rigid porous metal the outer surfaces of which wall portionsare mounted adjacent that part of the aircraft which it is desired toprotect from the formation of ice, said chambers each being formed froma channel-shaped metal member the outer part of which is filled with amass of rigid porous metal, the chamber being formed between the lowersurface of the porous metal and the bottom and lower sides of thechannelshaped member, a conduit substantially co-eX- tensive with saidseries of chambers for conveying fluid under pressure and flow resistingtubes connecting said conduit with said chambers the porosity of saidporous material being such that in the absence of said flow resistingtubes the fluid would not reach all said chambers.

7. In a system for distributing fluid over an extended surface, a seriesof chambers having wall portions of rigid porous material the outersurfaces of which wall portions constitute the surface to which saidfluid is to be delivered, a conduit substantially co-extensive with saidseries of chambers for conveying fluid under pressure, and flowresisting tubes connecting said conduit with said chambers the porosityof said porous material being such that in the absence of said fiowresisting tubes the fluid would not reach all said chambers.

8. In a system for distributing uld over an extended surface, a seriesof chambers having wall portions of porous metallic material the outersurfaces of which wall portions constitute the surface to which saidfluid is to be delivered,

a conduit substantially co-extensive lwith said reach all said chambers.

9. In a system for distributing fluid over an extended surface, achamber for fluid under pressure, a series of further` chambers eachhaving a material the outer surfaces of said wall portions each formingpart of the said extended surface, flow resisting tubes establishingcommunication between said first chamber and said, further chambersseverally, and` tubes larger than said flow resisting tubes surroundingthe discharge ends of said flow resisting tubes and serving to dispersefluid in said further chambers the porosity of said porous materialbeing such that in the absence of said flow resisting tubes the uidwould not reach all said chambers.

10. In a system for distributing uid over an extended surface, astructure comprising a conporous material lling the outer portion ofsaid channel the outer surface of which material forms the surface towhich said uid is to be distributed, partitions dividing the channelinto chambers, and flow resisting tubes leading from the conduit intosaid chambers severally the porosity of said porous material being suchthat in the absence of said flow resisting'tubes the fluid would notreach al1 said chambers.

portion of the wall thereof formed of rigid porous duit and a channelparalleling the conduit, rigidv 11. In a system for distributing a smallflow of fluid uniformly over a relatively large surface, a chamber forreceiving uid under pressure in excess of that permissible at thedistribution surface, a second chamber having a portion of the Wallthereof formed of rigid porous material, the outer surface of saidmaterial forming the surface to which the fluid is to be distributed,means dividing said second chamber into compartments, and flow resistingtubes establishing communication between said first chamber and thecompartments of said second chamber severally, the bores and lengths ofsaid tubes being such as to reduce theuid pressure at the porousmaterial to the desired extent the porosity of said porous materialbeing such that in the absence of said flow resisting tubes the fluidwould not reach all said chambers.

JOSEPH HALBERT. RONALD RAWSON RAWSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,129,977 I-Iagny Mar. 2, 19151,687,780 Neal Oct. 16, 1928 1,732,579 Gleason Oct. 22, 1929 2,075,659Ramsbottom et al. Mar. 30, 1937 2,097,926 Kimball Nov. 2, 1937 2,147,678Smith Feb. 21, 1939 2,155,592 Hardy Apr. 25, 1939 2,249,940 Bulloch July22, 1941 2,372,581 Jones Mar. 27, 1945

